Underwater acoustic analysis reveals unique pressure signals associated with aircraft crashes in the sea: revisiting MH370

Data analysis from the hydroacoustic stations of the Comprehensive Nuclear-Test-Ban Treaty Organization has unveiled distinctive pressure signals linked to aircraft crashes of varying sizes in the ocean. Notably, these signals were detected at distances ranging from two to five thousand kilometres, highlighting the efficacy of underwater acoustic technology in event identification and classification in marine environments. In this study, we investigate the plausibility of an aircraft, such as Malaysian Airlines Flight 370 (MH370), crashing into the sea leaving a discernible pressure signal at distant hydrophones. Consequently, we focus on recordings obtained from the hydroacoustic monitoring stations located at Cape Leeuwin and Diego Garcia, within a few minutes of the last satellite ping on the 7th arc, associated with the assumed crash time and location. Among the available data, only one relevant signal has emerged as a potential candidate, albeit recorded at a single station out of the two stations available. To ensure a comprehensive analysis, we also examine the time frame and location of the airplane along its initial route. Though no corresponding signal was observed. Nevertheless, the findings in this study narrow down the range of possibilities and present a novel scientific approach to investigate such incidents. These findings contribute to our understanding of acoustic signals associated with aircraft crashes at sea. They emphasise the potential for hydrophones to detect events even when the signal travels long distances through land. Ultimately, this research offers recommendations for conducting on-site experiments involving controlled explosions with energy levels similar to the impact of MH370 along the 7th arc. The aim is to encourage pertinent authorities to implement actions that could reveal insights into the destiny of MH370 specifically. Additionally, this initiative seeks to establish a comprehensive framework for addressing comparable incidents in the broader ocean context.


F-35A Stealth Jet Fighter
On April 9, 2019, a F-35A stealth jet fighter deployed in Japan crashed in the Pacific Ocean approximately 135 km east of Misawa Air Base in Aomori Prefecture, Japan, at 10:26:30 UTC (1).The coordinates of the crash site were approximately 40 o 30'10"N 142 o 04'37"E.The cause of the accident was attributed to spatial disorientation experienced by the pilot, which led to the loss of control of the aircraft.The aircraft impacted at the sea surface at about 300 m/s (1,080 Lion Air Flight 904 On April 13, 2013, Lion Air Flight 904, a Boeing 737-800, crashed into the sea while attempting to land at Bali's Ngurah Rai International Airport.The impact coordinates of the crash site were approximately 8 o 45'00.96"S115 o 09'01.01"E,and the impact time was around 07:10 UTC.The estimated impact speed of the aircraft was about 240 km/h.All 108 occupants survived the crash, but there were some injuries.Investigation revealed that the crash was caused by a combination of factors, including an incorrect approach procedure, pilot error, and problems with the aircraft's autothrottle system (6).

AB Aviation Flight 1103
On February 26, 2022, AB Aviation Flight 1103, a Cessna 208D Grand Caravan, crashed into the sea about 2.5 kilometres from Mohéli Bandar Es Eslam Airport in the Comoros.The crash occurred at around 09:30 UTC (12 o 14'36.3552'S43 o 46'50.6886"E.The crash resulted in the loss of all 14 occupants (7).

Air Asia Flight 8501
On December 28, 2014, Air Asia Flight 8501, an Airbus A320, crashed into the Java Sea while en route from Surabaya, Indonesia to Singapore.The crash occurred around 07:37 UTC and the impact coordinates of the crash site were approximately 05 o 50'36.0"S, 111 o 02'33.0"E. The estimated impact speed of the aircraft was about 274 km/h, with the aircraft's nose dipping down and hitting the water first.The crash resulted in the loss of all 162 aircraft occupants.Investigation into the accident revealed that the pilots' response to a malfunctioning rudder control system and their lack of understanding of the aircraft's systems contributed to the incident (8).

Asiana Airlines Flight 991
On July 28, 2011, Asiana Airlines Flight 991, a Boeing 747-400F cargo aircraft, crashed into the sea off Jeju Island while en route from Seoul, South Korea, to Shanghai, China.The crash occurred around 04:11 Korean Standard time (19:14 UTC on July 27, 2011) and the impact coordinates of the crash site were approximately 33 o 15'04.56"N, 124 o 59'31.02"E. Just before impact the aircraft speed reached 429 knots (795 km/h), though the estimated impact speed of the aircraft was about 442 km/h.The crash resulted in the loss of the only two occupants on board, the pilot and co-pilot.Investigation into the accident revealed that a fire developed on or near the pallets containing dangerous goods causing some parts of the fuselage to separate from the aircraft in midair (9).

ARA San Juan Submarine
On November 15, 2017, The ARA San Juan, a TR-1700-class diesel-electric submarine, operated by the Argentine Navy, went missing during a exercise mission.Despite extensive search efforts, the submarine was found only a year later in the Atlantic Ocean at a depth of 907 metres (2,976 ft) at 45 o 56'59"S 59 o 46'22"W 20 km north northwest from a seismic anomaly reported by the CTBTO (10).The incident resulted in the loss of all 44 crew members.
MH370: The disappearance stage: Gulf of Thailand & South China Sea MH370 departed Kuala Lumpur at 16:42 UTC, on 7 March 2014.Before reaching the Vietnamese border, waypoint IGARI, Kuala Lumpur air traffic control centre instructed the aircraft crew to contact the Vietnamese Control Centre, Ho Chi Minh.At 17:19 UTC the pilot-incommand of MH370 acknowledged the instructions by saying 'Good night Malaysia Three Seven Zero.', which was the last recorded radio transmission from MH370.After that time, any attempt to establishing communication with the crew had ended with failure.
At 17:22:57 UTC the aircraft was still en route, just a few seconds from performing the alleged sharp turn and go off route.The CTBTO hydroacoustic station H08 is at a distance of 3,800 km from the position of the aircraft, whereas H11 is as far as 6,900 km.Provided that an acoustic signal is travelling at an average speed between 1,450 m/s and 1,570 m/s, any signal from an impact should take between 40-43 minutes to reach H08 and 73-79 minutes to reach H11.Hence we are interested in signals that were recorded after 18:00 UTC, at H08 and 18:35 UTC at H11.However, note that since land separates the Gulf of Thailand and H08, the radiating signal could couple with the elastic seabed (as demonstrated in figure 7 top panel) travelling at a much faster speed of about 6,300 m/s during the 800 km inland journey, which would allow reaching H08S 7 minutes faster.Note that a wide spectrum of sound propagation speed has been considered to insure that include the entire spectrum of possible signals to ensures that no potential signal of interest is inadvertently overlooked (see Methods for more details).
The first observed signal is recorded at 17:54 UTC but only at H08S (figure S1 (a)).This signal is very weak, though its dispersion (illustrated in a white arrow), being similar to that associated with ARA San Juan, suggests an impulsive source much shorter than ARA San Juan signal recorded at H04S (figure 7 middle panel).Such an impulsive source generates signals of only a few seconds length, which makes measuring the bearing a challenging task (11).
Another signal is observed at 18:49 UTC, but again only at H08S (figure S1 (b)).The signal duration is at least twice as long compared to Lion Air Flight 904 (figure 5 (c), bottom panel), and about ten times longer than the signal from F-35a (figure 4 (a)).
The last observed signal of interest at H08S was recorded at 19:05 UTC (figure S1 (c)).Interestingly a corresponding signal has been also observed at H11S at 19:46 UTC (figure S1 (e )) with a bearing of 269 o towards the Gulf of Thailand.The shape of the two signals indicates an Signal observed (H11S)

Figure S1 :
Figure S1: Spectrogram and pressure time series of signals observed at H08S and H11S on 7 March 2014 shortly after the disappearance of MH370.White arrow indicates dispersion; panels (c) and (e), highlighted in magenta, might be of the same source.Signal in panel (c) has a bearing of 269 o relative to H11S, in the direction of the Gulf of Thailand.

Figure S2 :
Figure S2: MH370 civil radar flight path (orange curve); location of MH370 after last communication with pilot-in-command (white star); military radar flight path (yellow curve); location of the CTBTO's hydroacoustic stations H08S, H08N and H11S (white triangles); distance and bearing of source relative to H11S (solid magenta); bearing and distance of source relative to H08S (solid cyan); possible diffraction by land (green dashed oval); M 2.7 earthquake NE) Sinabang, Indonesia (green star).